Substrate for thermal boundary construction and method of making the same



3,285,518 TION AND METHOD Nov. 15, 1966 R. B. REID ETAL SUBSTRATE FOR THERMAL BOUNDARY CONSTRUC OF MAKING THE SAME 5 Sheets-Sheet 1 Filed May 8, 1961 ATTORNEY Nov. 15, 1966 B, EI ETAL. 3,285,518

SUBSTRATE FOR THERMAL BOUNDARY cousmucmou AND METHOD OF MAKING THE SAME Filed May a. 1961 5 Sheets-Sheet 2 INVEN 0R5 90667-6 5 ez'a 77le0d0m J Pricenskz' ATTORNEY Nov. 15, 1966 5, R ETAL 3,285,518

SUBSTRATE FOR THERMAL BOUNDARY CONSTRUCTION AND METHOD OF MAKING THE SAME 5 Sheets-Sheet 5 Filed May 19 INVENTORS err? 5. Reg

B 7/1 0120 re JPl'l'cem/ri AT TOR NE Y United States Patent SUBSTRATE FOR THERMAL BOUNDARY CON- STRUCTION AND METHOD OF MAKING Our invention relates to thermal boundary construction, and particularly to an improved wire plexus for use as a substrate in thermal boundaries, such as rocket nozzle liners and the like, and to a novel method of making the same.

In a copending application by Robert B. Reid, for Thermal Boundary Construction, which is assigned to the assignee of this application, a thermal boundary construction is disclosed which comprises a plexus of interconnected metal filaments coated with a refractory material. It is the object of the present invention to facilitate the manufacture of a plexus for this purpose, while improving the performance and increasing the life of this type of thermal boundary.

Our invention will be described with particular reference to rocket nozzles, since the liners for such nozzles present all of the problems encountered in other thermal boundaries. However, many other uses to which our invention can be put will be suggested to those skilled in the art as our description proceeds.

The corrosive incandescent gases to which a rocket nozzle is exposed require the nozzle to be made of a material both chemically inert and highly resistant to thermal shock. These conflicting requirements can be met successfully, in the manner described in the above mentioned copending application, by embedding a substrate of interconnected metal filaments in a matrix of refractory material. In such a construction, the inert, high melting refractory material forms the gas contacting surface, and the metal filaments serve to increase the physical strength of the nozzle, not only because of their inherent strength, but because they reduce the thermal gradients through the layer nearest the hot gas stream and thereby reduce thermal shock, at the same time inhibiting the propagation of any thermally induced cracks in the refractory material and holding in place any fragments that might otherwise be broken off.

The extent of the advantages obtained by the'construction described in the above copending application depend in large part on the intricacy of the metal plexus used as the substrate, and on the amount of metal that can be incorporated without making the plexus unduly stiff The intricacy of the plexus is important, because the shorter the path through the refractory between a given filament and the next, the more efiicient is the plexus, both in lowering the thermal gradient from the gas stream to the body of the rocket, and in inhibiting the propagation of cracks. The more metal that can be included, the better, since a high-melting metal such as tungsten best meets the requirements of a nozzle material, except in the surface layer which is subject to erosion, and in the necessary heat insulation between the nozzle liner and the body of the rocket. The plexus should not be made unduly stiff, because the thermal expansion or contraction of the ele- 3,285,518 Patented Nov. 15, 1966 ments of the plexus should be independent. For example, a solid annular ring of metal would be an undesirable substrate, because it might tend to warp as a unit in a way that would fragment the refractory material.

Numerous constructions might be devised which would, in principle, meet all of the requirements of a successful plexus outlined above. However, to produce such constructions in quantity, without an exhorbitant expenditure of time and money, could present a diflicult problem. In accordance with our invention, the problem is solved by using a novel process involving simple procedures and little equipment, which results in a plexus of greatly improved life and performance, and one that can be designed for maximum efliciency in the regions of greatest thermal stress.

Briefly, the novel process of our invention comprises interlinking helical coils of wire arranged in a parallel array, in a simple sequence of steps, in such a way that the coils are tightly interconnected in areas of maximum thermal stress, and have protruding unlinked portions in areas of lesser thermal stress; placing transverse strands of wire across the protruding ends; and interlinking the protruding ends with the transverse strands by helical coils of wire threaded through the protruding ends. The novel plexus produced by this process is highly intricate, and has a high concentration of metal in the areas of maximum thermal stress.

The process of our invention, and the novel product produced thereby, will best be understood by reference to the accompanying drawings, together with the following detailed description, of a preferred embodiment thereof.

FIGURE 1 is a schematic diagram illustrating the first step in the production of a plexus in accordance with our invention;

FIGURE 2 is a schematic diagram illustrating the sec- "ond step in the production of a plexus in accordance with the production of a plexus in accordance with our invention;

FIGURE 5 is a schematic diagram illustrating the fourth and fifth steps in the production of a plexus in accordance withour invention;

FIGURE 6 is a pictorial view, with areas enlarged, illustrating the general appearance and certain detailed aspects of a plexus in accordance with our invention; and

FIGURES 6A and 6C are enlarged, fragmentary views of a section of the plexus according to our invention.

FIGURE 6B is an enlarged, fragmentary view of the inner section of the plexus of our invention.

FIGURE 7 is a cross-sectional view, with a portion enlarged, of a rocket nozzle in accordance with our invention.

FIGURE 7A is an enlarged, fragmentary, cross-sectional view of a section of the internal throat of the embedded plexus in accordance with our invention.

Referring now to FIGURE 1, the first step in the production of a plexus in accordance with our invention is the manufacture of a plurality of subassemblies made by threading an elongated helical coil of wire 1, of a first length, into two shorter coils 2 and 3 of a second length, the first coil being carried through coils 2 and 3 until it protrudes on the other side as shown.

Next, as shown in FIGURE 2, two subassemblies are arranged side by side and interconnected by threading a coil 4 of the first length through adjacent shorter coils of the subassem'blies. The plexus 5, formed by repeating this process and adding subassemblies, can be continued to any desired length.

The next step in the formation of an annular plexus in accordance with our invention requires a suitable mandrel complementary in shape to the surface comprising the thermal boundary to be formed. FIGURE 3 shows a hyperboloida-lmandrel suitable for use in making a plexus for a rocket nozzle. As shown, it comprises a lower member 6 secured to an upper member 7 by a bolt 8 extending through a central aperture. in members 6 and 7. A washer 9 is placed over the end of bolt 8 and secured by a suitable means such as a nut 10 engaging threads formed on bolt 8.

Referring now to FIGURE 4, in conjunction with FIG- URES 2 and 3, the plexus is next wrapped around the mandrel and its end coils 2 and 3 are jointed by threading an additional coil 12 of the first length through their turns to form a closed link comprising the central portion of the plexus, which portion is now completed and forms the strongest and most intiricate portion of the structure, since it is in the region of the nozzle throat at which the maximum stress and erosion occur.

Referring now to FIGURE 5, the mandrel is next secured in a suitable rotatable chuck 13, and transverse strands of wire 14 and 15 are wound across the protruding ends of coils 1, 4, and 12. The winding may be started by securing one end of each of wires 14 and 15 to any of the coils 1, 4 and 12 by a single turn around it, and then continued by rotating chuck 13 to take wire from a spool 16 rotatably disposed on a shaft 17 and adapted to be moved along shaft 17 in the direction of the arrows. Similarly, wire 15 is drawn from a spool 18 slidably and rotatably disposed on a shaft 19.

When the winding is completed, essentially as shown for the portion overlying element 6 of the mandrel, transverse windings 14 and 15 are cut, and may be secured at the end of any of the protruding coils 1, 4 and 12 by aturn. It may be noted at this point that the only reason for using diflerent reference numerals to distinguish coils 1, 4 and 12 is to aid in visualizing the process by which they were assembled, since in physical respects these coils may be identical.

After the winding of strands 14 and 15 hasv been com.- pleted, the transverse strands are secured to the longitudinal coils 1, 4 and 12 by threading coils 20 through their turns and around the transverse strands at each intersection. Coils 20 are each of the length of a protruding end of one of coils 1, 4 and 12 on one side of the central portion of the plexus 5.

FIGURE 6 shows, in a somewhat schematic and pictorial fashion, the general appearance of a completed plexus in accordance with our invention. As shown, the central portion of the plexus comprises a tightly interlinked mass of wire formed by the interlinked turns of coils 1, 2, 3, 4 and 12. No attempt has been made to show these interlinkings in detail, but the general texture is indicated in the enlargement of FIGURE 6B.

The lower portion 21 of the plexus has been. distorted in FIGURE 6 to more clearly illustrate its construction, and in FIGURE 6A the manner in which transverse strands 14 are held in place by coils 20 threaded through coils 1 and 4 is pictorially illustrated.

As shown in FIGURE 6A, if desired in certain areas, the entrance and exit portions of the plexus can be reinforced by longitudinal strands 22 inserted through coil 1 and 20 and held between the turns of these coils and transverse strands 14. This permits the addition of additional metal in a very simple manner.

If desired, .the outer rims of the entrance and exit por- 4 tions can be further reinforced by weaving transverse strands 23 and 24 in and out of the coils.

When completed, the plexus is removed from the mandre-l by removing nut 10 and pulling members 6 and 7 apart.

Referring now to FIGURE 7, the completed plexus 5 is embedded in a layer of refractory material 25 to form a solid nozzle liner, as by flame spraying of the refractory material on the plexus, and the completed liner may then be attached to a refractory member 26, which serves both as as heat insulator and as a means of attaching the nozzle to the rocket. If desired, as described in the above mentioned copending application, the plexus may be coated with refractory material While in place on form 26, and the nozzle thus formed integrally in one step. The enlargement in FIGURE 7A shows somewhat pictorially a cross section through, the refractory material 25, illustrating the manner in which the individual coils contribute to the distributions of metal through a relatively thick layer nearest the gas contacting surface of the refractory 25.

The wire used to form the plexus of our invention may be of any suitable physically strong high melting metal, such as tungsten or the like, and the refractory material used to coat the plexus may be any of the known refractories, such as graphite, hafnium carbide, boron nitride, titanium carbide, titanium boride, tantalum carbide, or solid solutions of hafnium and tantalum carbide, in powdered form.

While we have described only one embodiment of our invention, in detail, many changes and variations will be apparent to those skilled in the art, and such may obviously be made withoutdeparting from the scope of our invention.

Having thus described our invention, whatv we claim 1s:

1-. A wire plexus for use as a substrate in a thermal boundary, comprising in combination: a ring of helical coils arranged side by side and having adjacent coils interlinking, certain of said coils protruding from at least one end of the ring; a coil of wire wound transversely around said ends; and helical coils interlinking said protruding ends and transverse wire.

2. A rocket nozzle liner, comprising, in combination: a refractory annular body having an entrance portion, an exit portion and a throat portion intermediate said entrance and exit portions, and a metallic wire plexus embedded in said body, said plexus comprising a first set of helical coils extending longitudinally along the contours of the nozzle from the entrance to the exit portion, a second set of helical coils joining adjacent members of said first set by interlinking their turns in the throat portion of the nozzle, a coil of wire wound transversely over said first set of coils in the entrance and exit portions-of the nozzle, and a third set of helical coils interlinking the intersections of the transversely wound coil and the coils of the first set in the exit portion of the nozzle.

3. A hyperboloidalplexus, comprising a first set of helical coils extending longitudinally along the contours of a hyperbolcid, a second set of helical coils shorter than said first set joining adjacent members of said first set by interlinking their tu-rns intermediate their ends, coils of wire wound transversely over said first set of coils on either side of said second set, and a fourth set of helical coils interlinking the turns of the first set and the transversely wound coils.

4. A reinforced rocket nozzle throat comprising: a cylindrical series of parallel, helical coils of refractory metal wires, each of the coils. in the series having adjacent turns interlinked; an annular ring of refractory metal; said cylindrical series of parallel helical coils of wirealbeing embedded in said annular ring of refractory met (References on following page) References Cited by the Examiner UNITED STATES PATENTS Emerson et a1 140--92.3 Wright 140-926 5 Fairweather 29-157 Kornar 29--157 Brenner 60--35.6 Ward 60-35.6 Lowe 60-35.6 0

FOREIGN PATENTS 492,687 3/1919 France. 1,112,030 11/1955 France.

122,968 2/1919 Great Britain.

MARK NEWMAN, Primary Examiner. HYLAND BIZOT, SAMUEL LEVINE, Examiners.

DONLEY I. STOCKING, J. B. HOBART, C. R.

CROYLE, Assistant Examiners. 

4. A REINFORCED ROCKET NOZZLE THROAT COMPRISING: A CYLINDRICAL SERIES OF PARALLEL, HELICAL COILS OF REFRACTORY METAL WIRES, EACH OF THE COILS IN THE SERIES HAVING ADJACENT TURNS INTERLINKED; AN ANNULAR RING OF REFRACTORY METAL; SAID CYLINDRICAL SERIES OF PARALLEL HELICAL COILS OF WIRE BEING EMBEDDED IN SAID ANNULAR RING OF REFRACTORY METAL. 